1. Field of the Invention
The present invention relates generally to fabrication of sliders for disk drive heads, and more particularly to the forming of the air-bearing surface of the sliders using photoresist techniques.
2. Description of the Prior Art
Data is stored and retrieved from a computer disk drive by positioning a magnetic read/write head over a rotating magnetic data storage disk. The magnetic heads are positioned close to one or more rotating disks containing magnetic material which records the information in concentric data tracks defined on surfaces of the disks, which are typically arranged in stacks. The head, or heads, which are also typically arranged in stacks, read from or write data to the disks. The heads are included in structures called “sliders” into which the read/write sensors are imbedded during fabrication. The write head operates to write data onto the disk by aligning magnetic poles of data bits of the magnetic material. A read head reads data by sensing the alignment of these data bit poles. Because the magnetic fields are very small, it is important that the read and/or write head is located very near the surface of the disk. Heads are typically fabricated as part of air bearing sliders which are specifically shaped so that the movement of the disk relative to the slider will provide a lifting force to cause the slider to fly above the disk when upon an air-stream existing close to the surface of the rotating disk.
Magnetic heads are usually fabricated as part of sliders either at the end of one or both of the side rails (also called pads) of the slider, or at a position near the center of the back end of the slider. The front end of the slider typically flies higher than the rear end, which aids in establishing air flow into regions of positive pressure, which act to lift the slider. This also allows the heads to be positioned closer to the disk surface. The lower surface of the slider is generally known as the Air Bearing Surface (ABS), and the shape of this ABS is critical to several different parameters which affect slider and head performance. The shape of this ABS has become the object of increasing subtlety and sophistication so that there may be areas of negative pressure which produce a slight “suction” effect which can be used to counter positive pressure in other portions of the ABS. The contour established is thus a matter of some precision and delicacy.
In order to shape this ABS contour, the typical procedure in the art involves using photoresist material to mask certain areas from the effects of shaping tools such as ion milling beams, and leaving other areas exposed for shaping. However, there have been certain problems encountered with the use of certain commercial photoresist materials.
Slider air-bearing patterning processes currently use relatively thick photoresist coating (>10 micrometers) to provide shallow etch wall profiles for improved lift characteristics. Liquid-apply photoresists are advantageous for this application because their usage avoids the fence formation that can contribute to particle formation in the drive. However a thick liquid photoresist process can be problematic due to cracking of the resist film. Cracking of the brittle thick photoresist material occurs during the baking step and is most pronounced in the gaps between sliders. These cracks produce irregular surfaces in the photoresist masks which can cause scattering of the exposure beams. Small manufacturing defects, known “reflective notching defects” or “mouse bites” are produced when scattered exposure beams erode portions of the edges of the pads. The sliders produced from this exposure have ABS pads with unacceptably high edge roughness that require scraping of the part. Yield loss as high as 10% due to this problem has been observed.
FIG. 1 (prior art) shows the air bearing surface of a slider 2 having a main body 3 and two pads 6, 7 also called side rails. The read/write head 4 is shown to be centrally disposed in a center platform 5 in this example, but may also be disposed at the end of one of the side rails or pads 6, 7. The pads 6, 7 and indeed the entire lower surface of the slider are very carefully designed for precise flow of air along the air bearing surface ABS 9. There are generally areas of positive pressure created when air flows over raised areas, such as the pads 6, 7 and there are also negative air pressure areas which serve to draw portions of the slider towards the surface of the disk and stabilize the flight of the slider.
FIGS. 2-7 show steps in the fabrication process of the prior art, with the production of reflective notching defects. In FIG. 2 (prior art), the photoresist material 14 is applied to the unshaped block 12 of material, which is to be formed into the slider, and then baked. It is during this baking process that the cracks of the cracked area 24 and surface irregularities develop as shown in FIG. 3 (prior art). The cracks are greatly exaggerated for sake of illustration in the figure, and it is commonly observed that the cracks are actually more numerous near the outer edges of the slider. Thus the placement and magnitude of the cracks are not to be taken as limitations, but serve only to illuminate the discussion.
FIG. 4 (prior art) shows the next step in the process. After the photoresist is baked, a pattern mask 15 is applied to the photoresist 14, which will serve to shield portions of the photoresist material 14 from light exposure. Again, the figure has been greatly simplified with only two areas of the pattern mask 15 shown, corresponding to the two side rails or pads 6, 7 (see FIG. 1), which will be formed. It will be understood that in practice, the pattern mask 15 is more spatially removed from the surface of the photoresist layer 14, generally with a lens (not shown) between pattern mask 15 and the photoresist layer 14 to focus the pattern onto the surface of the photoresist 14. For the sake of simplifying the illustration, the lens has been omitted from the figure and the pattern mask 15 draw in closer proximity to the photoresist layer 14 than is realistic.
Light beams 10 strike the photoresist 14, and the pattern mask 15, and wherever the light beams 10 strike the uncovered photoresist 14, the photoresist 14 is exposed. The photoresist 14 thus exposed becomes soluble to developer and can be removed in the following step. Ideally, the pattern mask 15 will form protected areas 16 in photoresist material 14, leaving the exposed portions 18 uncovered, which will later be removed. Dashed boundary lines 13 show the intended boundaries of the protected areas 16.
Defects arise when light beams 10 strike cracked areas 24 and are reflected or scattered into the protected regions 16, making unintended exposed areas 19. Scattered beams 21 are shown striking angled surfaces in the cracked area 24, forming unintended exposed areas 19 which extend past the dashed boundary line 13 into the protected areas 16.
FIG. 5 (prior art) shows the next step in which developer has been applied and the pattern mask 15 (see FIG. 4), and both intended exposed areas 18 and unintended exposed areas 19, have been removed. The developed photoresist pattern 25 thus covers portions of the unshaped block 12, but the protected areas 16 do not extend to the dashed line boundary 13, as intended.
In FIG. 6 (prior art), the developed photomask 25 and unshaped block 12 are subjected to a milling source 26, preferably ion milling beams 28. The developed photomask 25 creates protected areas 29 of the slider block 12 and intentionally exposed areas 30 of the slider block 12, as well as unintentionally exposed areas 31. The ion milling beams 28 remove exposed material in both intentionally exposed areas 30 and unintentionally exposed areas 31, thus creating the reflective notching defects 8 shown in the shaped slider structure 32 seen in FIG. 7 (prior art). Again, it is to be understood that the defects are shown greatly exaggerated and much more regular in configuration that those commonly experienced, but they have been simplified for purposes of illustration. If the defects are severe enough, the entire slider may have to be discarded as defective.
Thus there is a need for a method of fabrication and a treatment for photoresist mask material which can reduce scattering of the light beams during exposure, and thus reduce reflective notching defects.